Macadamia yield and quality responses to phosphorus

Abstract

Phosphorus fertiliser was applied to mature macadamia trees on 3 plantations with relatively low soil P in south-eastern Queensland at rates of 0, 10, 20, 40, 80, 160, and 320 kg P/ha at El Briale and Como Park and 0, 15, 30, 60, 120, 240, and 480 kg P/ha at Haylock. High rates of P were being applied to macadamias throughout the Australian industry and this study was designed to provide a basis for determining optimum application rates and critical soil P levels. Soil P was 33–199.5, 38.1–267.0, and 62.3–253.0 mg/kg at El Briale, Como Park, and Haylock, respectively. A tentative critical soil P concentration of 84–88 mg/kg was indicated, based on relative yields at El Briale and Haylock. Yield responsiveness to applied P was greatest at Haylock on a heavy soil that may have adsorbed P more readily, and had a higher P buffer capacity, than the lighter soils at the other sites. Leaf P was unresponsive to applied P, and hence soil P in this study. This is of concern since leaf P is used extensively to guide nutrition management. Further work is required to clarify relationships between leaf and soil P concentrations.